U.S. patent number 3,701,255 [Application Number 05/084,087] was granted by the patent office on 1972-10-31 for shortened afterburner construction for turbine engine.
This patent grant is currently assigned to United Aircraft Corporation. Invention is credited to Stanley J. Markowski.
United States Patent |
3,701,255 |
Markowski |
October 31, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
SHORTENED AFTERBURNER CONSTRUCTION FOR TURBINE ENGINE
Abstract
An afterburner construction for a turbine engine, such as a
turbofan engine, which is foreshortened by using a construction
which utilizes swirl flow phenomena to rapidly mix the engine
products of combustion and coolant flow, such as fan air, and/or to
rapidly accomplish the afterburning combustion process in the
afterburner, while maintaining engine performance and structural
part integrity.
Inventors: |
Markowski; Stanley J. (East
Hartford, CT) |
Assignee: |
United Aircraft Corporation
(East Hartford, CT)
|
Family
ID: |
22182805 |
Appl.
No.: |
05/084,087 |
Filed: |
October 26, 1970 |
Current U.S.
Class: |
60/762 |
Current CPC
Class: |
F23R
3/18 (20130101); F23R 3/22 (20130101); F23R
3/20 (20130101); F01D 5/18 (20130101); F01D
9/04 (20130101) |
Current International
Class: |
F23R
3/20 (20060101); F23R 3/02 (20060101); F23R
3/18 (20060101); F23R 3/22 (20060101); F01D
5/18 (20060101); F01D 9/04 (20060101); F02k
003/10 () |
Field of
Search: |
;60/261,39.36,39.69,39.72R,39.74R ;431/173,350 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hart; Douglas
Claims
I claim:
1. An afterburner having:
A. an afterburner duct having an axis and defining an afterburner
chamber therewithin,
B. means to pass fluid through said afterburner chamber in a
swirling flow pattern,
C. a cascade of radially extending, airfoil shaped vanes each
having a convex side and concave side, said vane positioned
concentrically about said axis within said afterburner chamber with
the vanes shaped so that adjacent vanes define a passage
therebetween which has an upstream portion which defines a passage
which is in substantial alignment with the direction of fluid flow
passing through the afterburner chamber and which has a downstream
portion which defines a passage substantially in alignment with the
axis so that the vanes serve as straightening vanes for the fluid
flowing therebetween, and so that the concave side and convex side
of adjacent vanes form concave and convex walls of said passage,
respectively,
D. a radially extending flameholder member positioned at each
passage upstream portion adjacent the passage concave wall so as to
establish a stagnation zone downstream thereof in said passage
adjacent said concave wall,
E. means to pass fuel into said passage to form a fuel-fluid
mixture passing over said flameholder,
F. means to ignite said fuel-fluid mixture to establish combustion
in said zone within said passage adjacent said concave wall to
establish outside-inside burning within said passage progressing in
the direction from the concave wall to the convex wall.
2. Apparatus according to claim 1 wherein said flameholder member
is of generally airfoil cross-section and includes a pivotable door
member attached to the side thereof away from said passage concave
wall and pivotable between a first non-afterburning position
wherein it cooperates with the remainder of the flameholder member
to define an airfoil cross-section and a second, afterburning
position where it extends into the passage to increase the size of
the stagnation zone.
3. Apparatus according to claim 2 wherein said door member is
perforated.
4. Apparatus according to claim 3 and including trigger means
located on said door member to physically disturb the interface
between the products of combustion of the stagnation zone and the
fuel-fluid mixture.
5. Apparatus according to claim 1 wherein said fuel injection means
comprises a plurality of radially extending spray bars located in
said afterburner chamber upstream of said passage.
6. Apparatus according to claim 1 wherein said fuel injection means
comprises conduit defining means positioned in the flameholder
means and shaped to communicate with said passage through a series
of spaced apertures.
7. Apparatus according to claim 1 wherein said fuel injection means
comprises conduit defining means extending radially in each vane
and including a radially extending pattern of apertures opening
into said passage through said concave wall.
8. Apparatus according to claim 1 and including flamespreader means
interconnecting said flameholder means.
9. Apparatus according to claim 1 and including diffuser means
upstream of said flameholder and vanes in said afterburner chamber
to reduce the axial velocity but not the spin velocity of the
swirling fluid passing through the afterburner chamber.
10. Apparatus according to claim 1 wherein said flameholder means
is spaced from said convex wall so that a cooling fuel-fluid
mixture passes therealong and is positioned in closely spaced
relation to said concave wall so that cooling fuel-fluid mixture is
metered therebetween to pass at high velocity along said concave
wall.
11. An afterburner having an axis and including:
A. an afterburner case concentric about the axis, and defining an
afterburner chamber therewithin,
B. a plurality of radially directed, circumferentially oriented
vanes each having a convex side and concave side, said vanes
forming a vane cascade extending across at least a part of said
afterburner chamber, wherein said vanes are airfoil shaped such
that adjacent vanes define a passage and combustor therebetween
with the concave side of one vane forming a concave wall of the
passage and the convex side of the adjacent vane forming a convex
wall of the passage, and such vanes being selectively shaped so as
to define the inlet portion of said passage to extend substantially
in the direction of intended fluid flow and the outlet portion of
passage extending substantially along said axis,
C. a radially extending flameholder of airfoil cross-section
positioned adjacent but in spaced relationship to the concave wall
of said passage at the inlet portion thereof to define a metering
passage for cooling fluid between said flameholder and said concave
wall,
D. means to pass fluid through said afterburner,
E. means to inject fuel into said fluid upstream of said
passage,
F. means to ignite said fuel-fluid mixture downstream of said
flameholders to establish pilot combustion in the stagnation zone
formed downstream thereof so that the products of combustion have a
density, .rho..sub.1, and a tangential velocity V.sub.t1, and so
that the unvitiated fuel-fluid mixture has a density, .rho..sub.2,
and tangential velocity V.sub.t2 to establish the product parameter
ratio .rho..sub.1 V.sub.t1.sup.2 > .rho..sub.2 V.sub.t2.sup.2 to
thereby accelerate intermixing and combustion between the
unvitiated fuel-fluid mixture and the pilot products of
combustion.
12. Apparatus according to claim 11 wherein said flameholder is of
generally airfoil cross-section and includes a pivotable door
member attached to the side thereof away from said passage concave
wall and pivotable between a first nonafterburning position wherein
it cooperates with the remainder of the flameholder member to
define an airfoil cross-section and a second, afterburning position
where it extends into the passage to increase the size of the
stagnation zone.
13. Apparatus according to claim 12 wherein said door member is
perforated.
14. Apparatus according to claim 13 and including trigger means
located on said door member to physically disturb the interface
between the pilot products of combustion and the fuel-fluid
mixture.
15. Apparatus according to claim 11 wherein said fuel injection
means comprise a plurality or radially extending spray bars located
in said afterburner chamber upstream of said passage.
16. Apparatus according to claim 11 wherein said fuel injection
means comprises conduit defining means positioned in the
flameholder and shaped to communicate with said passage through a
series of spaced apertures.
17. Apparatus according to claim 11 wherein said fuel injection
means comprises conduit defining means extending radially in each
vane and including a radially extending pattern of apertures
opening into said passage through said convex wall.
18. Apparatus according to claim 11 and including flame-spreader
means interconnecting said flameholder means.
19. Apparatus according to claim 11 and including diffuser means
upstream of said flameholders and vanes in said afterburner chamber
to reduce the axial velocity but not the spin velocity of the
swirling fluid passing through the afterburner chamber.
20. Apparatus according to claim 11 wherein said flameholder means
is spaced from said convex wall so that a cooling fuel-fluid
mixture passes therealong and is positioned in closely spaced
relation to said concave wall so that cooling fuel-air mixture is
metered therebetween to pass at high velocity along said concave
wall.
21. An afterburning having:
A. an afterburner duct having an axis and defining an afterburner
chamber therewithin,
B. means to pass fluid of density .rho..sub.1 through said
afterburner chamber in a swirling flow pattern with tangential
velocity V.sub.t1,
C. a cascade of radially extending, airfoil shaped vanes each
having a convex side and a concave side said vanes being positioned
concentrically about said axis within said afterburner chamber with
the vanes shaped so that adjacent vanes define a passage
therebetween which has an upstream portion which defines a passage
which is in substantial alignment with the direction of fluid flow
passing through the afterburner chamber and which has a downstream
portion which defines a passage substantially in alignment with the
axis so that the vanes serve as straightening vanes for the fluid
flowing therebetween, and so that the concave side and the convex
side of adjacent vanes form concave and convex walls of said
passage, respectively,
D. a radially extending flameholder member positioned at each
passage upstream portion adjacent the passage concave wall so as to
establish a stagnation zone downstream thereof in said passage
adjacent said concave wall,
E. means to pass fuel into said passage to form a fuel-fluid
mixture passing over said flameholder,
F. means to ignite said fuel-fluid mixture to establish pilot
combustion in said stagnation zone within said passage adjacent
said concave wall with the products of combustion having a density
.rho..sub.2 and tangential velocity V.sub.t2 wherein .rho..sub.1
V.sub.t1 > .rho..sub.2 V.sub.t2 to establish outside-inside
burning within said passage progressing in the direction from the
concave wall to the convex wall.
22. An afterburner having:
A. an afterburner duct having an axis and defining an afterburner
chamber therewithin,
B. means to pass fluid of density .rho..sub.1 through said
afterburner chamber in a swirling flow pattern with a tangential
velocity V.sub.ti ,
C. a cascade of radially extending, airfoil shaped vanes each
having a convex side and a concave side said vanes being positioned
concentrically about said axis within said afterburner chamber with
the vanes shaped so that adjacent vanes define a passage
therebetween which has an upstream portion which defines a passage
which is in substantial alignment with the direction of fluid flow
passing through the afterburner chamber and which has a downstream
portion which defines a passage substantially in alignment with the
axis so that the vanes serve as straightening vanes for the fluid
flowing therebetween, and so that the concave side and the convex
side of adjacent vanes form concave and convex walls of said
passage, respectively,
D. a flameholder member connected to the leading edge of each vane
and projecting therefrom into said passage to define a stagnation
zone downstream thereof.
23. Apparatus according to claim 22 wherein said flame holder
member is a flat, perforated member.
24. Apparatus according to claim 1 wherein said flameholder member
comprises a radially extending hollow duct of airfoil cross-section
positioned upstream of and interdigitated between each adjacent
vane and having aperture means in at least one wall of the trailing
edge thereof oriented substantially laterally, and including means
to pass a fuel-rich, heated, fuel-air mixture through said
flameholder to be discharged substantially laterally therefrom
through said apertures to ignite upstream of said passage when
brought into contact with said fuel-air mixture to serve as a pilot
flame to establish combustion in the fluid-mixture passing through
each passage of said vane cascade.
25. Apparatus according to claim 1 wherein said flameholder member
comprises a radially extending hollow duct of airfoil cross-section
positioned upstream of and interdigitated between each adjacent
vane and having aperture means in at least one wall of the trailing
edge thereof oriented substantially laterally, and including means
to pass fuel through said flameholder to be discharged
substantially laterally therefrom through said apertures to be
ignited upstream of said passages to serve as a pilot flame to
establish combustion in the fuel-fluid mixture passing through each
passage of said vane cascade.
26. Apparatus according to claim 24 wherein said aperture pattern
is located in both walls of the flameholder member on opposite
sides of the trailing edge thereof to establish an enlarged pilot
combustion zone downstream thereof.
27. In an afterburner having an axis:
A. an afterburner casing concentric about the axis and defining an
afterburner chamber therewithin,
B. a cascade of radially extending, airfoil shaped vanes each
having a convex side and a concave side said vanes being positioned
circumferentially within said afterburner combustion chamber and
shaped to define passages therebetween with the concave surface of
each vane defining a concave wall of said passage and the convex
surface of the vane defining a convex wall of said passage and with
said vanes so shaped and oriented that the inlet portion of said
passages extends in the direction of fluid flow through the
afterburner and the outlet portion of said passage extends in the
direction of the axis so that the vanes serve as fluid
straightening vanes,
C. means to pass fluid through said afterburner chamber to
establish a tangential velocity so that the fluid enters the
passage substantially in alignment with the direction of the
passage inlet,
D. means to inject fuel into said fluid upstream of said vanes to
establish a fuel-fluid mixture passing through said passages,
E. flameholder means in the form of radially extending hollow
members of airfoil cross-section interdigitated between said vanes
and positioned between said fuel injection means and said vane
inlet and having a plurality of apertures at the trailing edge
thereof extending substantially normal to the direction of fluid
flow, and
F. means to inject a hot, fuel-rich, fuel-fluid mixture into said
hollow flameholder means and through said apertures substantially
normally to said direction of fluid flow so as to ignite when
coming in contact therewith to establish a combustion pilot flame
downstream of said flameholder members and into said passage to
establish combustion of said fuel-fluid mixture in said
passage.
28. Apparatus according to claim 27 wherein the density of the
fuel-fluid mixture is .rho..sub.1 and its tangential velocity is
V.sub.tl , and further, wherein the density of the products of
combustion of the pilot flame is .rho..sub.2 and its tangential
velocity is V.sub.t2 and wherein product parameter .rho..sub.1
V.sub.t1.sup.2 > .rho..sub.2 V.sub.t2.sup.2 .
29. Apparatus according to claim 27 and including trigger means
associated with said flameholder means to physically disturb the
interface between said pilot flame products of combustion and said
fuel-fluid mixture.
30. Apparatus according to claim 29 wherein said trigger means
comprises an interrupted aperture pattern at the trailing edge of
said flameholder means.
31. Apparatus according to claim 29 wherein said trigger means
comprises at least one projection or indentation in the trailing
edge of the flameholder means.
32. Apparatus according to claim 16 wherein said vanes are of
substantially hollow construction and have an open radially outer
end which is of minimal radial distance from the axis at the vane
leading edge and maximum radial distance from the axis at the vane
trailing edge and including:
A. means to cool vanes including:
1. means to pass a coolant along the outer periphery of said
afterburner chamber at a location to be intercepted by the hollow
ends of said vanes,
2. a plurality of flow turning vanes positioned across the open
outer ends of each of said hollow vanes and shaped to define
passages therebetween which intercept said coolant and change the
direction of flow thereof into the hollow interior of said
vanes,
3. means to discharge said coolant flow into said afterburner
chamber at a station of lesser radius than the vane open outer
end.
33. Apparatus according to claim 32 and wherein said vanes overlap
circumferentially.
34. Apparatus according to claim 32 wherein said hollow vanes have
a concave wall and a convex wall and with said concave wall facing
generally in a downstream direction and wherein each vane also
has:
A. a coolant inflow manifold extending across the opened outer end
of said vane to collect all coolant flow entering said vane,
B. a coolant outlet manifold located at a blade inner radial
station,
C. a separator member attached to the interior of the blade leading
edge and the interior of the blade trailing edge and extending
therebetween and between the coolant inlet manifold and the coolant
outlet manifold to divide the interior of the blade into two
parallel, radially directed passages, and wherein said separator
member is located closer to said convex wall than said concave
passage extending between the coolant inlet and outlet manifold and
with the separator member and the vane convex wall defining the
boundaries thereof, and further wherein said second parallel
coolant passage extends between said coolant inlet and outlet
manifolds and is defined between said blade concave wall and said
separator means which define closely spaced walls and having:
1. a corrugated member extending between said concave wall and said
separator means with the corrugations thereof extending
substantially in a radial direction so as to cause the coolant flow
to scrub against said concave wall,
D. a plurality of said discharge slots located in said coolant
outlet manifold to discharge said coolant into said afterburner
chamber.
35. Apparatus according to claim 32 and having an inner body of
general circular cross-section positioned concentrically about said
axis, being hollow in construction and connected to the inner
radial end of each of said vanes with the vane interiors being in
communication with the interior of inner body, said body having at
least one slot in the wall thereof and wherein said hollow vanes
have a concave wall and a convex wall and with said concave wall
facing generally in a downstream direction so that all coolant flow
passing through said vanes and into said inner body are discharged
into said afterburner chamber through said slots.
36. Apparatus according to claim 35 and including separator means
in the interior of each vane selectively shaped to control the
amount of coolant flow which flows along the interior of said
concave and said convex walls.
37. An annular combustion chamber having an axis and having:
A. coannular duct members concentric about said axis and defining
an annular chamber therebetween,
B. means to pass fluid through said annular chamber in a swirling
flow pattern,
C. a cascade of radially extending, airfoil shaped vanes each
having a convex side and a concave side said vanes being positioned
concentrically about said axis within said annular chamber with the
vanes shaped so that adjacent vanes define a passage therebetween
which has an upstream portion which defines a passage which is in
substantial alignment with the direction of fluid flow passing
through the annular chamber and which has a downstream portion
which defines a passage substantially in alignment with the axis so
that the vanes serve as straightening vanes for the fluid flowing
therebetween, and so that the concave side and convex side of
adjacent vanes form concave and convex walls of said passage,
respectively, and with the vanes being shaped so that said concave
and convex walls of each passage are positioned substantially about
a common center of curvature.
D. a flameholder member positioned and shaped to establish a
stagnation zone downstream thereof in said passage adjacent said
concave wall,
E. means to pass fuel into said passage to form a swirling
fuel-fluid mixture passing over said flameholder, and
F. means to ignite said fuel-fluid mixture to establish combustion
in said zone within said passage adjacent said concave wall to
establish outside-inside burning within said passage progressing in
the direction from the concave wall to the convex wall.
38. Apparatus according to claim 37 and including means to cool
said vanes.
39. Apparatus according to claim 37 wherein said flameholder member
is a radially extending perforated plate member pivotally attached
to the leading edge of each vane and pivotally between an operative
position wherein it cooperates with the vane concave wall to define
the stagnation zone and a retracted position wherein it
substantially abuts the vane concave wall.
40. Apparatus according to claim 37 wherein said flameholder member
is a radially extending member of airfoil cross-section positioned
at the inlet of said passage adjacent each vane concave wall and
selectively shaped therefrom to define a cooling fluid metering
passage therebetween and having a fixed portion and a movable
portion wherein said movable portion comprises:
A. a radially extending and perforated plate member pivotally
attached to the flameholder fixed portion and pivotally between an
operable position wherein it cooperates with the flameholder fixed
portion to define said stagnation zone downstream thereof and a
retracted position wherein it cooperates with said fixed portion in
defining a radially extending member in airfoil cross-section.
41. Apparatus according to claim 37 wherein said fluid passing
means is a concentric mixer comprising:
A. a first duct of substantially circular cross-section supported
concentrically about said axis and defining a first passage
therewith as communicating between said mixer and said annular
combustion chamber, a second duct enveloped within said first duct
and being of substantially circular cross-section and concentric
therewith so as to cooperate with said first duct in defining an
annular passage therebetween and so as to define a second passage
therewithin, means to pass first swirling stream of a first fluid
of density .rho..sub.1 and tangential velocity V.sub.t1 through
said second passage into said first passage to establish a product
parameter .rho..sub.1 V.sub.t1.sup.2 , means to pass a second
swirling fluid stream through said mixer annular passage into said
first passage to establish an interface between said swirling
fluids and with the second fluid being of density .rho..sub.2 and
tangential velocity V.sub.t2 to establish a product parameter
.rho..sub.2 V.sub.t2.sup.2 which is less than the product parameter
.rho..sub.1 V.sub.t1.sup.2 to accelerate mixing between said first
and second fluids.
42. Apparatus according to claim 37 wherein said fluid passing
means is a barberpole mixer positioned upstream of said annular
combustion chamber and including:
A. an inner duct concentric about said axis to define a first
passage therewithin,
B. a second duct concentrically enveloping said first duct and
cooperating therewith to define an annular passage
therebetween,
C. means connecting said second duct to the outer coannular duct of
said annular combustion chamber,
D. a conical separator duct extending between said first and second
ducts and having an upstream end connected to said first duct and a
downstream end connected to said second duct, and having:
1. a plurality of slots located circumferentially thereabout and
each being disposed helically with respect to said axis and of
selected number, size and spacing to define the total slot area and
with said total area of the slots being a function of the
cross-sectional area of the first passage,
2. a scoop member enveloping each slot,
E. means to pass a first swirling fluid through said first passage
and a second fluid through said slots to mix as a swirling flow
mixture in said connecting means.
43. An afterburner having:
A. an afterburner duct having an axis and defining an afterburner
chamber therewithin,
B. means to pass a fuel-fluid mixture through said afterburner
chamber in a selected swirling flow pattern,
C. a cascade of radially extending, airfoil shaped vanes each
having a convex side and a concave side said vanes being positioned
concentrically about said axis within said afterburner chamber with
the vanes shaped so that adjacent vanes define a passage
therebetween which has an upstream portion which defines a passage
which is in substantial alignment with the direction of the
fuel-fluid mixture flow passing through the afterburner chamber and
which has a downstream portion which defines a passage
substantially in alignment with the axis so that the vanes serve as
straightening vanes for the fluid flowing therebetween, and so that
the concave side and convex side of adjacent vanes form concave and
convex walls of said passage, respectively, and with said vanes
shaped so that the concave and convex walls of each passage have
substantially a common center of curvature,
D. flameholder means shaped and positioned to establish a
stagnation zone in said passage adjacent said concave wall,
E. means to ignite said fuel-fluid mixture to establish combustion
in said zone within said passage adjacent said concave wall to
establish outside-inside burning within said passage progressing in
the direction from the concave wall to the convex wall.
44. Apparatus according to claim 43 and including means to cool
said vanes.
45. Apparatus according to claim 43 wherein said vanes are hollow
and include at least one aperture near the radially inner end
thereof and toward the forward portion thereof, and including means
to pass cooling fluid through the interior of said vanes for
discharge through said apertures.
46. Apparatus according to claim 43 wherein said vanes are hollow
and including a hollow inner body positioned concentrically within
said afterburner duct and said cascade of vanes to cooperate with
said duct in defining an annular passage in which said vanes are
located, said inner body having discharge slots forward of said
vanes, and means to pass coolant flow through said vanes into said
inner body and out of said discharge slot.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application contains subject matter related to the following
two applications assigned to the same assignee: (1) Application
Ser. No. 84,086, filed concurrently herewith for "Annular
Combustion Chamber for Dissimilar Fluids in Swirling Flow
Relationship" and (2) Application Ser. No. 84,088, filed
concurrently herewith for "Combustion Chamber Having Swirling
Flow".
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to afterburner construction and more
particularly to the construction for an afterburner which is
intended for use with a turbojet engine, possibly a turbofan
engine, so as to shorten the axial length of the afterburner,
thereby reducing engine length and weight.
2. Description of the Prior Art
In the prior art, attempts have been made to more rapidly mix the
products of engine combustion and the turbofan air upon entering an
afterburner, such as Howald U.S. Pat. No. 3,048,376 and Pierce U.S.
Pat. No. 2,978,865, however, these patents provided tortuous,
narrow passages through which the exhaust gas and the fan air must
pass and this created substantial losses in the system with
attendant engine thrust reduction.
Other patents, such as Ferri et al. U.S. Pat. No. 2,755,623, have
suggested the use of circumferentially rotating flow in combustion
chambers to permit the accomplishment of combustion in a shorter
axial distance, however, they do not suggest the use of swirling
flow principles to accelerate the mixing between two
thermodynamically and aerodynamically dissimilar fluids.
In my invention, swirling fluid flow principles are used in a vane
cascade in the afterburner to serve the function of accelerating
the mixing and combustion in the combustion zone of the afterburner
and also the function of straightening flow prior to discharge of
the exhaust nozzle. These afterburner vanes have cooling provisions
and may be used with many forms of fuel injection and fuel ignition
systems.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an
afterburner of minimal axial dimension or length.
It is an important feature of this invention to reduce the length
of an afterburner by passing swirling air therethrough and between
at least one cascade of selectively contoured vanes which are
positioned circumferentially about the afterburner chamber and
which serve as combustors when fuel is injected into the air at a
station upstream thereof to form a fuel-air mixture which is
ignited with flameholder support at the side of the vane defined
passage having the greater radius of curvature to thereby perform
the afterburning function and the flow straightening function in
the combustors defined between the vanes.
A further feature of this construction is that numerous fuel
injection mechanisms, flameholder mechanisms and interface
disturbing trigger mechanisms can be used therewith and the
construction includes provisions for keeping the vane walls
cool.
It is a further object of the present invention to teach apparatus
to shorten the length of an afterburner utilizing swirl flow by
placing a cascade of flow straightening vanes about the periphery
of the afterburner and positioning aerodynamic flameholders
immediately upstream or at the leading edge thereof and
interdigitated with respect thereto to establish a pilot combustion
zone for the fuel-air mixture being passed through the vane cascade
for curved flow combustion within the cascade.
It is a further object of this invention to teach apparatus for
shortening an afterburner by utilizing circumferentially positioned
and radially directed vanes to form a vane cascade, in combination
with flameholder and fuel injection mechanism to define pilot
combustors between the vanes, and wherein the vanes are hollow and
include provisions for cooling the vane wall, in particular the
substantially downstream directed concave vane wall in
installations where structural part cooling is necessary.
It is a further teaching of this invention to utilize either a
concentric mixer or a barberpole mixer upstream of my cascade
flameholder in an annular combustion chamber. While the cascade
flameholder can be used in a turbojet engine, in a duct heater
engine, and in turbofan engines, it is particularly attractive when
used with a mixed turbofan cycle engine because a concentric or
barberpole mixer can be utilized forward of the cascade flameholder
to mix the fan and engine streams and provide this mixture to the
cascade in the proper swirl flow relationship, so that accelerated
mixing and combustion will take place within the cascade
simultaneously with the cascade performing the function of
straightening the direction of fluid flow to an axial
direction.
In accordance with one of the features of the present invention,
the engine exhaust gas and the turbofan air entering the
afterburner are controlled by means of guide vanes or the like so
that as they enter the afterburner through a concentric mixer, the
product parameter .rho..sub.1 V.sub.t1.sup. 2 of the engine exhaust
gases is greater than the product parameter .rho..sub.2
V.sub.t2.sup.2 of the fan air where .rho. is density and V.sub.t is
tangential velocity, and further wherein trigger means are provided
to physically disturb the interface between the swirling streams of
engine exhaust gas and fan air entering the afterburner, and still
further wherein the afterburner may include a variable area exhaust
nozzle at the downstream end thereof and flow straightening vanes
upstream of the exhaust nozzle, and still further wherein said
trigger means may be circumferentially oriented and radially
extending corrugations or convolutions and/or axially extending
scallops attached to the downstream end of the splitter duct
between the engine exhaust gases and the fan air.
In accordance with still a further feature of the present
invention, the fan air and the engine exhaust gas of a turbofan
engine are mixed rapidly before or upon entering the afterburner in
a construction which utilizes a plurality of circumferentially
positioned and helically oriented three-dimensional scoop cascades
which intercept and deliver fan air through a plurality of
circumferentially positioned and helically oriented matching slots
in a splitter duct extending across the fan air stream, and wherein
the area of the duct system through which the engine exhaust gases
enter the afterburner has a selected relationship to the total slot
area so as to control the fan air velocity magnitude entering the
afterburner chamber and so that the scoop and slot shape
establishes a plurality of circumferentially oriented and
selectively spaced helical sheets of fan air penetrating and mixing
with the swirling engine products of combustion in a minimal axial
distance and with minimal mixing losses.
Other objects and advantages of the present invention may be seen
by referring to the following description and claims, read in
conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a showing of a turbofan engine with the afterburner
thereof partially broken away to illustrate the general environment
and location of my invention.
FIG. 2 is a showing of the combustion chamber area of an
afterburner utilizing a vane cascade flameholder to define the
combustion chamber.
FIG. 3 is a showing along line 3--3 of FIG. 2 of my cascade
flameholder in which the vanes of the cascade establishes
combustion chambers therebetween and serve flow straightening
devices, and in which the flameholder is a pivotable door attached
to the leading edge of the turning vanes.
FIG. 4 is a showing similar to FIG. 3 of a modification of my
cascade flameholder.
FIG. 5 is an enlarged, perspective showing of the flameholder
mechanism used in the FIG. 4 construction.
FIG. 6 is a perspective showing of the FIGS. 4-5 flameholder
mechanisms in their afterburning positions and connected by a
flamespreader.
FIG. 7 is a cross-sectional showing of the inlet portion of an
afterburner utilizing my combustion chamber defining and flow
turning vanes in combination with an aerodynamic flameholder to
form a cascade flameholder.
FIG. 8 is a view taken along line 8--8 of FIG. 7.
FIG. 9 is an enlarged cross-sectional showing of my aerodynamic
flameholder.
FIG. 10 is a cross-sectional showing of an afterburner utilizing a
flameholder and vane construction generally of the type shown in
FIG. 2 but wherein the vanes are hollow and have cooling
provisions.
FIG. 11 is an enlarged showing of one of the hollow vanes of the
FIG. 10 construction.
FIG. 12 is a view taken along line 12--12 of FIG. 11.
FIG. 13 is a view taken along line 13--13 of FIG. 11.
FIG. 14 is a cross-sectional showing of an afterburner with a
central portion thereof removed to illustrate the use of the fan
air duct and the splitter duct as concentric mixers alone or with a
cascade flameholder.
FIG. 15 is a view taken along line 15--15 of FIG. 2 and showing
radially extending corrugations as trigger means on the splitter
duct.
FIG. 16 is an alternate form of trigger means and is illustrated as
axially extending scallops at the trailing end of the splitter
duct.
FIG. 17 is an illustration of one of the vane cascades of the FIG.
14 construction shown in variable positionable form.
FIG. 18 is a partial showing of the afterburner inlet utilizing a
"barberpole" mixer.
FIG. 19 is an unrolled showing of the tapered separator duct which
extends across the fan-air passage to illustrate the helical slot
plurality used therein and to illustrate also the three-dimensional
hooded, vaned cascade used with these slots.
FIG. 20 is an alternate form of the tapered separator duct and the
vaned cascade and slot combination of the barberpole mixer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 we see turbine engine 10, which is shown to be
of the turbofan variety purely for the purpose of illustration but
it should be noted that the invention disclosed herein would have
application to any engine in which engine exhaust gas were
discharged into an afterburner, preferably in combination with
coolant gas. Engine 10 is generally of circular cross-section and
concentric about axis 12 and includes fan section 14, compressor
section 16, burner section 20, and turbine section 22, and
afterburner section 24. Variable area exhaust nozzle 26 is
preferably located at the downstream end of the afterburner to vary
outlet area in conventional fashion. Fan duct 28 is of circular
cross-section and positioned concentrically about axis 12 and
connects to afterburner duct 30 so as to conduct the fan air
directly into the afterburner. Engine casing 32 is positioned
concentrically within fan duct 28 and cooperates therewith to
define annular fan air passage 34 and envelops the engine
compressor section 16, burner section 20 and turbine section 22 and
culminates in or attaches to splitter duct 36, which envelops the
last stage 38 of turbine section 22 and projects into or toward the
afterburner chamber 40 formed within afterburner duct 30. Fan air
duct 28 and splitter duct or engine exhaust duct 36 form concentric
mixer 41. Fan air after passing through annular passage 34 flows
radially outwardly of splitter duct 36 and engine exhaust gas
flowing through passage 42, defined within splitter duct 36, flows
radially inwardly of splitter duct 36, and since both of these
fluids will be flowing in swirling fashion either due to the action
of the engine including turbine stage 38 and the action of the
blades of the fan section 14, or additional flow directing vanes
utilized therewith, an interface 44 will be established between
these two swirling fluid streams downstream of splitter duct 36. To
establish the desired swirling flow, it may be desirable to remove
or adjust the conventional flow straightening vanes downstream of
the turbine and the fan.
In the afterburner section 24, fixed inner body 46 is positioned
concentrically within afterburner duct 30 and vane cascade 48,
whose construction and function will be described in greater
particularity hereinafter, extends between afterburner duct 30 and
fixed inner body 46. Fuel injection means 50 injects fuel upstream
or forward of vane cascade 48 into the fan air exhaust gas mixture
to form a fuel-gas mixture therewith. Ignitor means (not shown) of
conventional design would be used to initiate combustion in
combustion zone 58.
In operation, the products of combustion enter the afterburner
through passage 42 and intermix with the fan air which enters the
afterburner through passage 34. Fuel is injected by injector 50 and
combustion takes place in the combustion zone 58 and 40 and the
products of combustion thereof, in a vitiated state, are then
discharged to atmosphere through variable area exhaust nozzle 26 to
perform a thrust generating function.
It is an important feature of my invention to shorten the
afterburner combustion zone proper by utilizing a cascade
flameholder of the constructions shown in FIGS. 2-13, and this
cascade flameholder may be used with or independently of the mixer
configurations shown in FIGS. 14-20 if the engine is a turbofan
cycle.
Referring to FIGS. 2 and 3 we see afterburner chamber 40 defined
within afterburner duct 30 and with variable area exhaust nozzle 26
at the downstream end thereof. If required, afterburner duct will
include a cooling liner 90 of cylindrical shape and concentric
about axis 12 which defines a cooling air annular passage 92 with
duct 30. Cooling liner 90 performs the function of distributing the
available cooling air selectively over the entire length of the
afterburner and uses conventional means, such as louvers or
transpiration cooling, to perform this function. Vane cascade
flameholder 48 consists of a plurality of radially extending and
circumferentially oriented vanes 94 with flameholder member 96
utilized therewith. As previously described, fuel injection
mechanism 50 are shown as radial spray bars in FIGS. 2 and 3 and
inject atomized fuel into combustion chamber 40 to be carried with
the swirling gas through the vane cascade flameholder 48 for mixing
and combusting therewithin. The vane cascade and the flameholders
96 preferably extend radially across annular passage 43 defined
between inner body 46 and the afterburner outer case 30 or liner 90
and constitute a circumferential row or cascade of vanes. These
vanes are shown in greater particularity in FIG. 3 wherein it will
be noted that adjacent vanes 94 define passage 110 therebetween and
the vanes are so shaped that the inlet or upstream portion 112 of
passage 110 opens in the direction of the swirling approach flow V,
while the downstream portion 114 of passage 110 extends in the
direction of axis 12 so that vanes 94 serve as straightening vanes
as well as forming combustors therebetween as soon to be described.
Passage 110 is defined between concave wall 116 of one of the vanes
94 and convex wall 118 of the adjacent vane 94 so that these walls
become the walls of passage 110. It will be noted that flameholder
mechanism 96 is a extending plate member which preferably extends
for the full radial dimension of vanes 94 and is pivotally attached
to vane 94 at its leading edge at pivot station 126 so that by any
convenient means, such as the construction shown in FIG. 17 to be
described hereinafter, the flameholder plate member 96 may be
pivoted between the FIG. 3 solid lines, afterburning positions
where they cooperate with vanes 94 to form recirculation zone 128
and a retracted nonafterburner position in which they lay flat
against or recess into the concave surface 116 of vanes 94 so as to
present minimum drag during nonafterburning operation. Flameholder
members 96 include a plurality of apertures 148 extending
therethrough in a radially extending row or pattern so as to permit
the fuel-air mixture to pass therethrough into recirculation zone
125 downstream thereof for ignition and burning in zone 125 to form
a pilot combustion zone, and the remainder of the fuel-air mixture
passing through passages 110. It will be noted that the hot
combustion gases 128 from the pilot 127 flow along the concave side
of passage 110 parallel to the flow of the nonvitiated fuel-air
mixture and serves to ignite the fuel-air mixture.
In operation, the fuel-air mixture formed by the plurality of fuel
spray bars 50 injecting into the passing air, enters passage 110 at
inlet section 112 in the downstream direction of flow V. It may be
considered that vanes 94 are curved about center of curvature 140
and that due to the swirling motion of the fuel-air mixture about
axis 12 as it enters chamber 110 and the subsequent straightening
of the flow as it progresses through passage 110, it is evident
that the flow is constrained by the vanes 94 to follow a curved
path in the plane of FIG. 3. Furthermore, an interface 44 is
established in this curved passage between the hot combustion
products 128 from the pilot burner 127 and the nonvitiated, cool,
fuel-air mixture flowing through the remainder of the passage as
shown in FIG. 3. Since the pilot gases are at a considerably higher
temperature and have experienced the losses associated with passing
through the flameholder holes and combustion, the
.rho.V.sub.t.sup.2 product of these gases is less than that of the
nonvitiated flow. As my copending U.S. Pat. application filed on
even date and entitled "Annular Combustion Chamber for Dissimilar
Fluids in Swirling Flow Relationship" fully explains, whenever two
fluids flow parallel to a curved interface in such a way that the
product parameter .rho.V.sub.t.sup.2 of the fluid at a smaller
radius is greater than the product parameter .rho.V.sub.t.sup.2 of
the fluid on the larger radius side of the interface, where V.sub.t
refers to that component of the gas velocity in the tangential
direction relative to the center of curvature of the interface, the
interface will be unstable and rapid mixing will occur. Such is the
case in passage 110 and this product parameter inequality
accelerates not only mixing between the cooler fuel-air mixture and
the products of combustion but burning of the nonvitiated fuel-air
mixture due to this rapid mixing. Even if combustion is not
completed in cascade 48 the interdigitated radially extending
sheets of hot gas and cooler fuel-air mixture in the duct
downstream of vanes 94 will promote completion of the combustion
within a short distance downstream of vanes 94. This vitiated
mixture is then discharged through outlet portion 114 in the
direction of axis 12 as nonswirling flow to be discharged in this
fashion to generate thrust through the variable area exhaust nozzle
26.
In the FIG. 3 construction, three fuel spray bars 50 are shown
positioned between adjacent vanes 94 and at one of the stations are
designated number 1, 2, and 3 for identification. For power control
purposes, the fuel spray bars 1, 2, and 3 can be progressively
flowed in response to increased engine power requirements. For
example, spray bar 1 would be used at all times during low power
afterburner operation and possibly also to maintain pilot
combustion zone 128 ignited at all times under circumstances where
immediate power increase might be required. In response to demand
for increased power, spray bar 2 would be flowed along with spray
bar 1 for intermediate afterburner operation, and in response to a
demand for maximum power, spray bars 1, 2 and 3 would be flow
simultaneously.
A modification of my cascade flameholder 48 is shown in FIG. 4
wherein vanes 94 form passages 110 as in the FIG. 3 construction.
It will be noted that flameholder mechanism 96 is a radially
extending member of airfoil cross-section which is located at the
inlet portion 112 of passage 110 and is selectively positioned from
vanes 94 to form metering slot 120 therebetween through which a
selected amount of cooling air is directed against the concave
surface 116 of vane 94 for cooling purposes.
Flameholder 96 is shown in greater particularity in FIG. 5 and is
of generally airfoil cross-section and includes stationary member
122 and pivotable door member 124 pivotally attached thereto along
radially extending hinge 126. Door member 124 is pivotable, and may
be actuated as shown in FIG. 17, between its FIG. 5 position, which
is its nonafterburning position, wherein the door member 124
cooperates with the fixed portion 122 of flameholder member 96 to
define a smooth, aerodynamic, low drag shape. As best shown in FIG.
6, door members are pivotable to an open or afterburning position
so as to cooperate with fixed portion 122 in defining a void cavity
128 therebetween. Fuel-air mixture enters this cavity through holes
148 in door 124. Conventional ignition means, such as spark plug
130 shown in FIG. 6, can be used to ignite the fuel-air mixture in
the pilot combustion zone 128 and it is preferable that
flamespreader 132, which is preferably a trough shaped ring, extend
circumferentially about axis 12 such that its hollow interior 134
is in communication with the hollow interiors 136 of flameholder 96
so as to assist in initiating combustion and spreading it to the
various radial pilot flameholders 96.
While the fuel injection means shown in FIGS. 2 and 3 is a
plurality of fuel spray bars, it will be noted by viewing FIG. 4
that the fuel injection means can well be a plurality of radially
extending conduits 160 located in the vane forward or upstream
portion at convex surface 118 and including a radially extending
hole pattern 168 through which fuel is injected for mixing with the
air entering passage 110. In addition to these two types of fuel
injection, as best shown in FIG. 5, the fuel injection means can be
a similar conduit member 166 extending radially through the fixed
portion 122 of flameholder 96 and includes an aperture pattern 168
communicating with passage 166 and passage 110 through which
atomized fuel is sprayed. The recessed flameholders 160 and 166
have an advantage over spray bars 50, in that they create no
drag.
Except for the different flameholder construction, the operation of
the cascade flameholder 48 shown in FIGS. 4 and 5 is as previously
described in connection with the FIG. 3 construction.
In any of these constructions, it may be desirable to provide
trigger means to physically disturb the interface between the
swirling, cooler, fuel-air mixture and the swirling, hot products
of combustion and trigger means may comprise physical projections
150, shown in FIGS. 5 and 6 extending from the outer periphery of
door member 124. To provide a smooth, low-drag, airfoil shape
during the nonafterburning mode of operation, indentures 154 may be
provided in the trailing edge 152 of stationary portion 122 of
flameholder 96 to receive trigger projections 150 in nested
relationship.
Another variation of cascade burning which may be used in my
foreshortened afterburner to accelerate combustion is shown in
FIGS. 7-9. Preferably, this configuration and the previously
described configuration may be used at the very forward end of the
afterburner chamber 40 downstream of a diffuser section 170 formed
between afterburner duct 30 and tapered inner body 46. The diffuser
action serves to reduce the axial component of the swirling flow
velocity, V.sub.x, but does not retard substantially the tangential
flow velocity V.sub.t. This aids in supporting combustion and
reduces the pressure loss associated with the combustion process.
In this modification, straightening vanes 94 are again used as in
the FIG. 2-4 constructions to receive the swirling fuel-air mixture
approaching in direction V and to straighten the flow thereof to be
in alignment with axis 12. However, a different flameholder and
fuel injection provision is included in the FIG. 7-9 embodiment. In
this embodiment, the flameholders 172 are of the aerodynamic type
and comprise a hollow airfoil shaped tube 174, shown best in FIG.
9, which extends substantially radially with respect to axis 12 and
which is interdigitated between adjacent turning vanes 94 so that
the wake 128 therefrom flows along concave surface 116 of vanes 94
and passages 110. Aerodynamic flameholders 172 include a pattern of
lateral apertures 176 on at least one side, and preferably both
sides thereof toward the trailing edge 178 thereof. In this
construction, hot air in some form and fuel are injected into the
hollow interior 180 of aerodynamic flameholder 172 to be injected
substantially laterally thereto through laterally directed slot
patterns 176 at sufficient velocity to disturb the flow passing the
vane and create a wide recirculation zone 125 downstream of each
aerodynamic flameholder to serve as a pilot flame for the fuel-air
mixture which is being passed through passages 110 by the injection
of fuel in any conventional manner such as the fuel spray bars 50
of the type disclosed in FIG. 2. The warm air for this fuel-air
mixture may be tapped through line 182 from upstream of the last
turbine stage 22 and fuel is added thereto from a fuel source
through line 184 with valves 186 and 188 determining the richness
of the fuel-air mixture. This mixture is made excessively rich so
that it will not burn until the mixture is diluted by mixing with
the flow in the afterburner duct after which it will spontaneously
ignite, burn and provide an ignition source for the fuel-air
mixture from fuel spray bars 50 entering passages 110. Accordingly,
accelerated mixing and burning takes place in combustor passages
100 due to the aforementioned product parameter difference which
occurs between the products of combustion and the nonvitiated
fuel-air mixture passing through combustor passage 110 in swirl
flow relationship. Again, in this construction, an irregular
aperture pattern of apertures 176 or selectively positioned
indentations or bulges, such as element 150 in FIG. 5, in the
trailing edge 178 of aerodynamic flameholder 172 will serve as
triggering means to physically disturb the interface between the
products of combustion and the nonvitiated fuel-air mixture to
further accelerate mixing therebetween.
In certain installations it is important to keep all parts which
are exposed to the atmosphere operating at a relatively reduced
temperature and this can be accomplished in my turning vane
combustor configuration 48 as best shown in the FIG. 10-13
modifications the cooling technique now to be described is
important to structural cooling, especially in afterburner
installations. As best shown in FIGS. 10-13, vanes 94 are hollow in
construction and have flow turning vane cascade 180 at their outer
edges which intercept the fan air and further include cooling air
discharge slots, such as slot 182 at a low static pressure region
closer to centerline 12 and toward the vane upstream stations. In a
turbojet installation, cooling air would preferably be ducted to
the vanes 90 from the compressor or elsewhere. Centerbody 46 may
also be hollow and the interior of vane 94 is in communication with
the hollow interior thereof such that coolant discharge may occur
through slots 184 in the hollow afterbody 46, preferably as far
upstream as possible to achieve maximum pressure differential
between the inlet to vanes 94 and the discharge slots. The FIG.
10-13 constructions can be generally of the type shown in
connection with FIGS. 3-9 but the details of the vanes 94 are
different to accommodate cooling. In this construction, it is
desirable that vanes 94 overlap circumferentially. As best shown in
FIG. 11, the fan air enters hollow vane 94 through flow turning
vane cascade 180 which is positioned to intercept fan air. Upon
entering the vane, the cooling air will flow directly to either or
both discharge slots 182 and 184 or, if selective cooling is
desired as to favor concave surface 116, which is exposed in a
downstream location and experiences a higher heat load during
augmented operation, the hollow interior of the vane 94 is
compartmentized as best shown in FIGS. 11-13. In this
compartmentized construction, the fan air, after passing through
turning vane cascade 180, enters inlet manifold 190 at the radial
outer vane location. Separator member 192 extends between the vane
leading edge 194 and the vane trailing edge 196 to separate the
flow entering inlet manifold 190 into a first hollow compartment
198 which includes convex wall 118 as one of its boundary defining
walls and the remainder of the air from manifold 190 enters second
compartment 200 which is of Finwall.sub.TM construction.
As best shown in FIG. 13, the inlet manifold 190 is divided by
separator 192 so that the bulk of the air entering the vane 94 is
directed into Finwall passage 200, while the lesser portion passes
through hollow passage 198. The Finwall construction is best shown
in FIG. 12 and includes spaced walls 116 and 202 which have
radially directed corrugated sheets 204 therebetween. This Finwall
construction provides large extended surfaces for the cooling air
to scrub against and remove heat from concave wall 116 of the
hollow vane to perform a maximum cooling function with respect
thereto. After passing through passages 198 and 200, the coolant is
then received in discharge manifold 206, which is hollow and runs
throughout the full vane axial dimension and is discharged
therefrom either through a plurality of slots 182 at an inner
radial station in the vanes or enters hollow inner body 46 for
discharge therefrom through slots 184, or both. Coolant flow is
insured in this fashion since in the swirling flow approaching the
vanes the static pressure increases with the distance from axis 12
and therefore slots 182 and 184 are located at minimal static
pressure stations while inlet 180 is at a point of maximum static
pressure and the radial pressure gradient across the swirling flow
provides the pressure differential to flow the cooling system.
While the FIG. 10-13 construction is shown in a turbofan engine
environment, it should be borne in mind that hollow, cooling vanes
in this cascade flameholder construction could be used in many
different kinds of engines. For example, the FIG. 10-13 cascade
flameholder could be used in a duct heater within the fan duct of a
turbofan engine or in an unmixed turbofan engine where unmixed fan
air provides the cooling air. In other engine applications, such as
a turbojet engine, the cooling air could be piped to the vane
interior from the engine compressor or other convenient pressure
source.
As best shown in FIG. 1, the configurations of FIGS. 2-13 may be
used to form the combustion zone of an afterburner.
In turbofan engines, higher nonaugmented (without afterburning)
thrust is achieved when the fan stream and the engine exhaust gas
stream are mixed and discharged through a common exhaust nozzle to
generate thrust. To reduce the overall engine length and weight, it
is desirable to reduce the afterburner length by accelerating this
mixing. Mixing acceleration can be achieved by the use of
concentric or barberpole mixers now to be described. These mixers
not only reduce afterburner length and weight but are well suited
for use with the previously described cascade burner 48 because the
exit flow therefrom is swirling and swirling inlet flow is a
requirement of the cascade flameholder.
A concentric mixer used in this environment is shown .rho.FIGS.
14-16 and it should be noted that the mixer is located upstream of
the previously described cascade flameholder 48.
Referring to FIG. 14 we see that fan air enters afterburner chamber
40 through annular passage 34 and the engine gases enter the
afterburner chamber 40 through annular passage 42 to establish
interface 44 therebetween. Both of these streams may be swirling
about axis 12 without further assistance, or by the removal of the
flow vanes which are conventionally located downstream of the fan
and turbine, however, it may be desirable to place a cascade of
turning vanes 60 in passage 34 and a cascade of turning vanes 62 in
passage 36 to establish the desired tangential velocities, V.sub.t,
of the swirling streams to accelerate mixing between the engine
exhaust gases and the fan air by establishing the mixing criteria
product parameter ratio .rho..sub.1 V.sub.t1.sup.2 > .rho..sub.2
V.sub.t2.sup.2, where .rho..sub.1 and V.sub.t1 are the density and
tangential velocity of the engine exhaust gas, respectively, and
.rho..sub.2 and V.sub.t2 are the density and tangential velocity of
the fan air, respectively. The theory of swirling flow intermixing
is explained in detail in my copending application filed on even
date and entitled "Annular Combustion Chamber for Dissimilar Fluids
in Swirling Flow Relationship", to which reference may be made.
With this product parameter ratio established, interface 44 is
unstable and intermixing between the engine exhaust gas and the fan
air is accelerated. To further accelerate this intermixing,
radially extending corrugations 66 may be positioned in the
splitter duct 36 at its downstream end. These convolutions
physically disturb the unstable interface 44 to further accelerate
the rate of intermixing between the engine exhaust gas and the fan
air. So as to hold flow loses to a minimum while accomplishing the
desired perturbation of the interface, it is important that
convolutions 66 extend over about 20 to 30 percent of the fan air
and engine gas streams.
In addition to, or as a substitute for, the radially extending
corrugations shown in FIG. 15, splitter duct 36 could be fabricated
to include axially extending scallops 68 shown in FIG. 16 which
will serve to physically disturb the unstable interface 44. Because
it is desirable to cause the exhaust gases to be discharged to
atmosphere through exhaust nozzle 26 in an axial flow direction, it
may be desirable to place a cascade of straightening vanes 70 in
the afterburner chamber 40 upstream of the exhaust nozzle.
Obviously, these vanes could be the previously discussed
flameholder vanes.
While the vanes of cascades 60 and 62 may be selectively shaped and
oriented and fixed in position, it may be desirable to make one or
both of them of the variable position type as shown in FIG. 17. In
the FIG. 17 construction, vane 60 is pivotally connected to
afterburner duct 30 and splitter duct 36 by pivot pin members 72
and 73 which extends from opposite ends thereof. Each vane 60
carries ring gear 75 at its outer end. Annular ring gear 78 is
supported for rotation about axis 12 by support ring 80 and has
matching gears matingly engaging the gears of each of the ring
gears 75 so that as annular gear 78 is caused to rotate about axis
12 by pilot manipulation in any convenient way, such as pilot
controlled linkage 82 which connects pivotally to annular gear 78
and is pivotally supported about pivot point 84, each of the ring
gears 75 and hence vanes 60 are caused to pivot about their axis in
unison to a new position so as to vary the flow angle and hence the
tangential velocity V.sub.t of the fluid flowing between the
vanes.
Another modification of the accelerated intermixing feature of my
afterburner is shown in FIGS. 18 and 20. As best shown in FIG. 18,
conical separator duct 70 is connected at its forward end to engine
case 32 and increases in radial dimension from axis 12 in a
downstream direction and attaches at its downstream end to fan case
28 so as to extend completely across the fan air passage 34. FIG.
19 shows conical separator member 70 in an unrolled condition and
it will be noted that it includes a circumferentially extending row
of slots 72, which slots are helically oriented with respect to
axis 12 and of selective spacing and numbering that the total area
defined by the slot plurality through which the fan air must pass
is matched to the cross-sectional area of annular passage 42
downstream of turbine stage 38 through which the engine exhaust
gases must pass so as to establish a selected velocity magnitude V
at which the fan air enters the afterburner chamber 40 through
slots 72. Three-dimensional scooped cascades 74 extend from each
slot and include hood member 76 which connects to separator 70 at
its after end and is open at its forward end to intercept fan air,
and which further includes a cascade of turning vanes such as 78
which cooperate with hood member 76 in intercepting the fan air
from passage 34 and cause the fan air to turn in direction smoothly
into the afterburner chamber 40 through slots 72 at a selected
tangential velocity V.sub.t. This construction is known as
"barberpole" mixer 71 in that swirling helical sheets of fan air
are caused to penetrate into the swirling engine exhaust gases due
to the action of the three dimensional vaned cascades and slots 72
to establish interdigitated streams of dissimilar fluids for
accelerated mixing therebetween. The connecting of vaned cascades
74 and slots 72 is selected so as to establish the mixing criteria
product parameter ratio .rho.V.sub.t.sup.2 (engine exhaust
gases)> V.sub.t.sup.2 (fan air) where .rho. is fluid density and
V.sub.t is fluid tangential velocity.
For ease of construction, it may be desirable to fabricate
separator 70 as shown in FIG. 20 so that it includes stepped
forward ends 96 in wall members 98, which cooperate with hood
members 100 to intercept and direct the flow of fan air into the
afterburner with the cooperation of the cascade of vanes 102. In
the FIG. 20 construction, the vanes are attached by welding or
other convenient means to the stepped front end 96 of the wall
members 98 and to hood member 100 to form the selectively shaped
passage 104 therethrough to determine the tangential velocity
V.sub.t at which the fan air is going to enter the helically
directed, spaced slots 72. As such, FIG. 20 represents a barberpole
mixer modification which may be simpler to fabricate.
It will be noted that in both the concentric mixer configuration
shown in FIGS. 14-16 and in the barberpole mixer configuration
shown in FIGS. 18 and 19 a swirling flow situation is created
within the afterburner passage 40 and this swirling flow condition
is a requirement for the inlet flow of the cascade flameholder 48
previously described in connection with FIGS. 2-13. Accordingly, as
best shown in FIG. 14, it is highly desirable to utilize either of
these mixers upstream of cascade flameholder 48 to accomplish
overall afterburner length reduction.
While I have illustrated and described my cascade flameholder 48 in
an afterburner environment as shown in FIGS. 2-13, it is important
to note that it has several additional applications. For example,
in the turbofan engine illustrated, the cascade flameholder 48 is
shown to be used in the mixed-flow afterburner, but it could also
be used as a duct heater by being selectively positioned in passage
34. My cascade flameholder could also be used in the main
combustion chamber or the afterburner of a turbojet engine, or
could, in fact, be used as an interburner between turbine stages,
or in any other environment which defines an annular passage in
which a change in the flow directions is desirable. The vanes of my
cascade flameholder act as straightening vanes in both the burning
and nonburning modes of operation and also serve as combustion
flameholders.
It will be evident to those skilled in the art that an afterburner
of my construction is foreshortened by the use of either the
concentric mixer or the barberpole mixer with the vane cascade
combustors taught herein and an advantage to a lesser degree will
also be achieved by using the mixers or the vane combustors by
themselves.
I wish it to be understood that I do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
* * * * *